Someone mentioned putting a single element lens on a bellows. Any ideas?

That works. One approach is to use +dioptre close-up optics on extension. A +10dpt meniscus becomes an uncorrected 100mm lens. (Effective aperture depends on diameter and mount.) A +8dpt Raynox DCR-250 becomes a somewhat corrected 125/3.2 lens. I'm playing with the front element from a Polaroid Pronto! camera, probably 60/2 although it's more like 60/2.5 the way I've mounted it. This meniscus gives a VERY soft and PF-full image, probably much more than you'd like. Of what I've used, the Raynox gives the most satisfactory results.

Of course, one old soft-focus trick is just to smear a clear filter with some Vaseline. Or nose grease.

That works. One approach is to use +dioptre close-up optics on extension. A +10dpt meniscus becomes an uncorrected 100mm lens. (Effective aperture depends on diameter and mount.) A +8dpt Raynox DCR-250 becomes a somewhat corrected 125/3.2 lens. I'm playing with the front element from a Polaroid Pronto! camera, probably 60/2 although it's more like 60/2.5 the way I've mounted it. This meniscus gives a VERY soft and PF-full image, probably much more than you'd like. Of what I've used, the Raynox gives the most satisfactory results.

Of course, one old soft-focus trick is just to smear a clear filter with some Vaseline. Or nose grease.

Yeah, I gave up on grease a while back. You have any sample SF photos from your setups to post?

I did think that if a guy is going the grease route to do this. Get a dedicated junk lens. Coat the filter on the *reverse side* and that way the grease will stay put as well as your effect from the grease as you like it to be. Just don't store it in the heat or the grease may run.

That works. One approach is to use +dioptre close-up optics on extension. A +10dpt meniscus becomes an uncorrected 100mm lens. (Effective aperture depends on diameter and mount.) A +8dpt Raynox DCR-250 becomes a somewhat corrected 125/3.2 lens. I'm playing with the front element from a Polaroid Pronto! camera, probably 60/2 although it's more like 60/2.5 the way I've mounted it. This meniscus gives a VERY soft and PF-full image, probably much more than you'd like. Of what I've used, the Raynox gives the most satisfactory results.

Of course, one old soft-focus trick is just to smear a clear filter with some Vaseline. Or nose grease.

Yow. That is expensive. I take it you don't already have a P645 bellows? One problem with using such a bellows is its depth. It probably doesn't compress to less than 40mm. Add the P645 register of almost 71mm, and you won't be able to achieve infinity focus with anything shorter than a 115mm optic. There's a solution: an M42 focusing helicoid. See below.

First, we need a lens mount. My usual budget approach would be to find some screw-->P645 adapter -- but I don't see any inexpensive ones of any kind on eBay. Mount-reversal ring, plain macro tubes... nada, nothing, zilch.

So my next starting move would be to look for a trashed lens, and remove its mount. Do any other MF bayonets physically fit the P645 mount? Lacking such, another possible starting point is a P645 body cap, and I *do* see one of those on eBay right now for ~US$30.

Next step: turn an adapter or salvaged mount or body cap into an M42-P645 adapter. If an existing adapter has threads, step rings can be used to get to M42. Otherwise, an adapter or salvaged mount can have a wide-flange M42-PK adapter glued to it. The body cap is even simpler: cut a hole in it, into which an M42 male thread will fit. I would insert a shortest M42 macro tube section, thread it into the hole, then glue it in place.

Now we skip the expensive and too-fat bellows and go lean: an M42 16-35mm focusing helicoid, about US$60 shipped from Shanghai to USA. Thread that into the M42 female mount we've attached to the adapter or body cap. On the front of that, add a step-up ring to get from M42 to the optic's diameter.

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What single element lens fits on the front of the bellows?

I suggested either a +10dpt close-up meniscus (FL=100mm) or a +8dpt Raynox DCR-250 (FL=125mm). With my 49mm +10dpt optic (US$10 shipped) I use a 42-49mm step-up ring. With the Raynox (rear thread is 43mm) I use a 42-43mm step-up ring. The Raynox gives better images. The meniscus is cheaper.

Yes, either optic will project an image circle large enough for the 645 sensor. For focusing, remember that you need register + extension = focal length to reach infinity focus, and more extension for closer work. Play with the M42 macro tubes to get the right mix.

Yow. That is expensive. I take it you don't already have a P645 bellows? One problem with using such a bellows is its depth. It probably doesn't compress to less than 40mm. Add the P645 register of almost 71mm, and you won't be able to achieve infinity focus with anything shorter than a 115mm optic. There's a solution: an M42 focusing helicoid. See below.

First, we need a lens mount. My usual budget approach would be to find some screw-->P645 adapter -- but I don't see any inexpensive ones of any kind on eBay. Mount-reversal ring, plain macro tubes... nada, nothing, zilch.

So my next starting move would be to look for a trashed lens, and remove its mount. Do any other MF bayonets physically fit the P645 mount? Lacking such, another possible starting point is a P645 body cap, and I *do* see one of those on eBay right now for ~US$30.

Next step: turn an adapter or salvaged mount or body cap into an M42-P645 adapter. If an existing adapter has threads, step rings can be used to get to M42. Otherwise, an adapter or salvaged mount can have a wide-flange M42-PK adapter glued to it. The body cap is even simpler: cut a hole in it, into which an M42 male thread will fit. I would insert a shortest M42 macro tube section, thread it into the hole, then glue it in place.

Now we skip the expensive and too-fat bellows and go lean: an M42 16-35mm focusing helicoid, about US$60 shipped from Shanghai to USA. Thread that into the M42 female mount we've attached to the adapter or body cap. On the front of that, add a step-up ring to get from M42 to the optic's diameter.

I suggested either a +10dpt close-up meniscus (FL=100mm) or a +8dpt Raynox DCR-250 (FL=125mm). With my 49mm +10dpt optic (US$10 shipped) I use a 42-49mm step-up ring. With the Raynox (rear thread is 43mm) I use a 42-43mm step-up ring. The Raynox gives better images. The meniscus is cheaper.

Yes, either optic will project an image circle large enough for the 645 sensor. For focusing, remember that you need register + extension = focal length to reach infinity focus, and more extension for closer work. Play with the M42 macro tubes to get the right mix.

That is some complex stuff. Thanks for the roadmap on putting it togther.

The bellows, providing I can find a 645 set, may be OK for me. I only shoot protraits and close up with soft focus. So infinity is not that big a deal.

With the bodycap option. I wonder if I could hook up my 100mm T mount soft focus to a hole in the the body cap?

That is some complex stuff. Thanks for the roadmap on putting it togther.

The biggest trick is finding or fabricating the right adapters. After that, it's just a matter of playing with rings and stuff until it all falls together. [/me looks warily at towering stack of rings & adapters teetering on the edge of /me desk]

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The bellows, providing I can find a 645 set, may be OK for me. I only shoot protraits and close up with soft focus. So infinity is not that big a deal.

I mention infinity because it may not be so far from there to a portrait distance (1-2m) depending on the optics. The +10dpt (100mm) meniscus option cuts it a bit close. The +8dpt (125mm) Raynox approach gives a bit more leeway.

Also, even cheaper than either bellows or helicoid, just use M42 macro tubes to set a comfortable fixed-focus distance. I use some 75mm enlarger lenses at 1m or 1.5m fixed-focus for portraits, no problem.

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With the bodycap option. I wonder if I could hook up my 100mm T mount soft focus to a hole in the the body cap?

Depending the thickness of the body cap, lens weight may be a limiting factor. I can put my helicoid, some tubes, and a small lens, on some thick caps. You'll have to see if your 100mm is light enough for stability.

If you get a thick enough cap, and carefully gouge a 42mm hole, you can screw both T2 and M42 threads into it (unglued). That may be your general-purpose adapter!

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Where do you buy the single element optics you mention?

eBay. Besides the +1+2+3dpt or +1+2+4dpt sets, are also +10dpt and even +20dpt closeup offerings. I haven't had the nerve yet to try a +20, and I already have three +10s, woo woo. You want distorted as well as soft? Get a +10dpt with 49mm thread, and a 49-49mm thread-reversal ring, and mount the meniscus backwards. Edges get weird...